Get the Specialized entry level full suspension Stumpjumper that sells for $2500. Full Suspension bikes are much more forgiving of user error or limitations. If you get a hardtail bike then have a dropper post added - you will be glad you did.
Do invest in a good mountain bike MIPS helmet and knee guards and gloves. A bad knee injury can take you out of action for several months and a broken collar bone takes 3-4 months to heal with adults.
I have found that everything I did on a road bike is the opposite on a mountain bike for the most part. A half day class would be a good investment.